In a traveling-wire electroerosion process, a continuous electrode wire is axially transported by a wire axial drive means from a supply means to a takeup means. In the path of wire travel, a pair of machining guide members are disposed at opposite sides of an electrically conductive workpiece to define a straight line path therebetween through which the electrode wire axially is passed while traversing the workpiece, thus positioning the electrode wire in a precise machining relationship with the workpiece. Tension means is provided to hold taut the traveling electrode wire across the supply and takeup sides and between the positioning guide means. An electrical machining current, typically or preferably in the form of a succession of time-spaced electrical pulses, is applied between the traveling electrode wire and the workpiece across a machining gap flooded with a machining liquid, e.g. a water liquid of a dielectric nature or low conductivity, or an aqueous solution or electrolyte, to electroerosively remove material from the workpiece. As the material removal proceeds, the workpiece is displaced transversely to the longitudinal axis or the straight line path of the traveling wire electrode along a prescribed two-dimensional machining feed path under the command, advantageously, of a numerical controller, so that a desired contour of machining is generated in the workpiece.
It is important that the wire electrode be of good electrical conductivity and composed so as to afford a satisfactory rate of material removal and yet be subject to less electroerosive wear itself. It is desirable that the wire electrode be heat-resistant and retain sufficient tensile strength at a temperature created by the passage of a machining current of high amperage or current density, to be free from breakage in operation. Customarily, the wire electrode is constituted as a single strand wire having a diameter of 0.05 to 0.5 mm composed of a copper metal or alloy such as brass. Such a wire has been provided by drawing it through a die and usually has had a circular cross section.
The machining liquid is supplied, typically from one or more nozzles, into the machining gap to serve on the one hand as a gap machining medium to carry the discharge and/or electrolytic current and on the other hand as a coolant to dissipate heat developed by the passage of the machining current of high amperage or current density required. Higher amperage or current density is desirable to achieve greater removal rate and efficiency, and necessitates removal of the machining liquid from the gap at a higher rate.
It has, however, been experienced that the continued supply of the machining liquid in an ample amount towards the machining gap often causes wire breakage and does not allow the use of a greater machining current. When the electrode wire is excessively heated or insufficiently cooled, it tends to break. There is thus a severe limitation in the heat-dissipation ability of a conventional electrode wire traversing the machining gap. With a conventional electrode wire having a regular machining surface, it has also been observed that gases produced by discharges and/or electrolytic decomposition of the delivered machining liquid tend to be adherent to the electrode surface to separate the latter from the coolant liquid and thus to act as a thermal insulator therebetween, and further to allow gaseous discharges essentially of a thermal nature to develop thereacross. Furthermore, a number of electrode wires of different thicknesses have had to be replaced by one after another depending upon particular configurations to be machined in a workpiece.